Resonant nanostructures for highly confined and ultra-sensitive surface phonon-polaritons

Alexander M Dubrovkin,Qi Jie Wang,Donguk Nam,Bo Qiang,Teddy Salim,Nikolay I Zheludev

doi:10.1038/s41467-020-15767-y

Alexander M Dubrovkin, Qi Jie Wang + Show 4 more

Open Access

https://doi.org/10.1038/s41467-020-15767-y

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Abstract

Plasmonics on metal-dielectric interfaces was widely seen as the main route for miniaturization of components and interconnect of photonic circuits. However recently, ultra-confined surface phonon-polaritonics in high-index chalcogenide films of nanometric thickness has emerged as an important alternative to plasmonics. Here, using mid-IR near-field imaging we demonstrate tunable surface phonon-polaritons in CMOS-compatible interfaces of few-nm thick germanium on silicon carbide. We show that Ge-SiC resonators with nanoscale footprint can support sheet and edge surface modes excited at the free space wavelength hundred times larger than their physical dimensions. Owing to the surface nature of the modes, the sensitivity of real-space polaritonic patterns provides pathway for local detection of the interface composition change at sub-nanometer level. Such deeply subwavelength resonators are of interest for high-density optoelectronic applications, filters, dispersion control and optical delay devices.

Highlights

Plasmonics on metal-dielectric interfaces was widely seen as the main route for miniaturization of components and interconnect of photonic circuits
As the “gold standard” high-index material for the fabrication of ultra-smooth, wafer-scale and low-loss nanometric coatings, Ge provides excellent conditions for support of high-quality mid-IR surface PhPs (SPhPs) modes. It allows the formation of surface oxidized layer (i.e. Ge oxide)[44,45], which gives us the opportunity to trace polaritons dynamics under chemical interactions with the environment. scattering-type scanning near-field optical microscopy (s-SNOM) technique here provides direct information on the changes in the SPhP wavelength and mode field distribution, which we model with evolution of the device material composition
Germanium structures have been fabricated on silicon carbide substrate using electron beam lithography (EBL), followed by 7 nm Ge layer deposition and liftoff processes

Summary

Introduction

Plasmonics on metal-dielectric interfaces was widely seen as the main route for miniaturization of components and interconnect of photonic circuits. The growth of large-scale high-quality uniform films, capable of supporting intrinsic hyperbolic modes, is a significant challenge[41], which limits phononic applications of the two-dimension materials to exfoliated-flake-based microscale devices Another approach of employing nearly isotropic polar crystals with ultra-thin dielectric or semiconductor-coating layers[22,23] revealed even larger-momentum PhPs at the crystal surface. We demonstrate deeply subwavelength planar resonators supporting extremely confined and tunable SPhPs on group IV semiconductor platform, consisting of silicon carbide substrate coated with a nanometric germanium film of deeply subwavelength thickness While this system enables ultracompact low-loss on-chip phononic devices with optical features more than two orders smaller than free-space wavelength (λ0), it bears the potential in wafer-scale fabrication compatible with CMOS technology

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